The frame structure under TDD (Time Division Duplex) mode in the LTE (Long Term Evolution) system is also called “Frame Structure Type 2”. FIG. 1 is a schematic diagram of this frame structure. As shown in FIG. 1, in this frame structure, a 10 ms (307200 Ts, 1 ms=30720 Ts) wireless frame is divided into two half-frames. The length of each half-frame is 5 ms (153600Ts). Further, each half-frame contains five sub-frames, and each sub-frame is 1 ms in length.
Table 1 shows the configuration of the uplink/downlink signals of each sub-frame in the frame structure as shown in FIG. 1. Wherein D denotes downlink sub-frames which are used for transmitting downlink signals; and U denotes uplink sub-frames (or called normal uplink sub-frames) which are used for transmitting uplink signals. Further, an uplink/downlink sub-frame is divided into two time slots with length of 0.5 ms each; and S denotes special sub-frames. A special sub-frame contains three special time slots, namely: a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS). In real systems, the uplink/downlink configuration indexes are informed to a User Equipment (UE) through broadcast messages.
The resource allocation in the LTE system takes a Physical Resource Block (PRB) or a Resource Block (RB) as a unit, wherein each PRB occupies 12 sub-carriers (or called Resource Element (RE), each sub-carrier is 15 kHz) in the frequency domain and occupies a time slot in the time domain, namely, it occupies SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols of 7 normal cyclic prefixes (normal CP) or 6 extended cyclic prefixes (extended CP) in the time domain. If the total number of RBs to which the uplink system bandwidth corresponds in the frequency domain is NRBUL, then indexes of the RB will be 0, 1, . . . , and NRBUL−1 and indexes of the RE will be 0, 1, . . . , and NRBUL·NSCRB−1, wherein NSCRB is the number of sub-carriers to which one RB corresponds in the frequency domain. Taking normal CP for example, the structure of the PRB is shown in FIG. 2. One PRB occupies 12 REs in the frequency domain and occupies 7 normal CPs in the time domain. The total number of RBs to which the uplink system bandwidth corresponds in the frequency domain is NRBUL, the indexes of the RB are 0, 1, . . . , and NRBUL−1, and the indexes of the RE are 0, 1, . . . , and NRBUL·NSCRB−1.
TABLE 1Configu-Switch-pointSub-frame numberrationperiod012345678905msDSUUUDSUUU15msDSUUDDSUUD25msDSUDDDSUDD310msDSUUUDDDDD410msDSUUDDDDDD510msDSUDDDDDDD65msDSUUUDSUUD
The bandwidth of Sounding Reference Signal (SRS) is configured by adopting a tree structure, namely, each kind of SRS bandwidth configuration corresponds to a tree structure, the tree structure is shown in FIG. 3. Wherein The SRS-bandwidth at the top layer corresponds to the maximum bandwidth of this kind of SRS bandwidth configuration. Tables 2 to 5 show the SRS bandwidth configuration in different uplink bandwidth range. Taking Table 2 for example, the number of RB is 6≦NRBUL≦40, wherein SRS bandwidth configuration is 1, b=0 is the first layer, and is the top layer of the tree structure, the SRS-bandwidth of this layer is the bandwidth to which 32 PRBs correspond and is the maximum SRS-bandwidth of the SRS bandwidth configuration; b=1 is the second layer, the SRS-bandwidth of this layer is the bandwidth to which 16 PRBs correspond, and one SRS-bandwidth of the upper layer is split into two SRS-bandwidths of the second layer; b=2 is the third layer, the SRS-bandwidth of this layer is the bandwidth to which 8 PRBs correspond, and one SRS-bandwidth of the upper layer is split into two SRS-bandwidths of the third layer; b=3 is the fourth layer, the SRS-bandwidth of this layer is the bandwidth to which 4 PRBs correspond, and one SRS-bandwidth of the upper layer is split into two SRS-bandwidths of the fourth layer. Tables 3 to 5 show the SRS bandwidth configuration respectively when the number of the RB is 40<NRBUL≦60, 60<NRBUL≦80 and 80<NRBUL≦110. Further, the sub-carriers of the SRS signals in the same SRS frequency band are placed alternately, this structure is shown in FIG. 4, and this comblike structure allows more users to send SRS signals in the same SRS-bandwidth.
TABLE 2(6 ≦ NRBUL ≦ 40)SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthSRS bandwidthb = 0b = 1b = 2b = 3configurationmSRS, bNbmSRS, bNbmSRS, bNbmSRS, bNb03611234341132116282422241464141320145414141614441415121434141681424141741414141
TABLE 3(40 < NRBUL ≦ 60)SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthSRS bandwidthb = 0b = 1b = 2b = 3configurationmSRS, bNbmSRS, bNbmSRS, bNbmSRS, bNb04812421224314811638242240120245413361123434143211628242524146414162014541417161444141
TABLE 4(60 < NRBUL ≦ 80)SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthSRS bandwidthb = 0b = 1b = 2b = 3configurationmSRS, bNbmSRS, bNbmSRS, bNbmSRS, bNb0721243122431641322162442601203454134812421224344811638242540120245416361123434173211628242
TABLE 5(80 < NRBUL ≦ 110)SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthSRS bandwidthb = 0b = 1b = 2b = 3configurationmSRS, bNbmSRS, bNbmSRS, bNbmSRS, bNb0961482242461961323162442801402202453721243122434641322162445601203454164812421224374811638242
With respect to the above-showed SRS bandwidth configuration, when the SRS-bandwidth allocated to a UE is smaller than the maximum SRS-bandwidth, frequency hopping should be adopted so that all frequency bands within the range of the maximum SRS-bandwidth have opportunities to transmit SRS. As frequency hopping arithmetic is based on SRS transmission times, therefore, SRS transmission times require continuous increment. Further, in order to make the frequency hopping process controllable, then requires the UEs with the same SIRS period have same SRS transmission times at the same time.
With respect to the TDD system, the SRS signal transmission position of the UE is informed by a base station through UE specific signaling. UE specific signaling refers to that this signaling is sent to a specific UE only. The base station informs UE specific SRS period and sub-frame offset configuration index to UE, each configuration index corresponds to a period and sub-frame offset, the condition to which this configuration corresponds is shown in Table 6.
TABLE 6Configuration Index, ISRSSRS Period (ms)SRS Sub-frame Offset020, 1120, 2221, 2320, 3421, 3520, 4621, 4722, 3822, 4923, 410-145ISRS-1015-2410ISRS-1525-4420ISRS-2545-8440ISRS-45 85-16480ISRS-85165-324160ISRS-165325-644320ISRS-325 645-1023reservedreserved
In Table 6, the meaning of SRS Sub-frame Offset may include the following two circumstances.
Circumstance 1, the SIRS period is 2 ms:
(1) Sub-frame offset Noffset is 2, 3 and 4, representing the first, second and third uplink sub-frames in a half-frame respectively;
(2) When there are two SC-FDMA symbols in the UpPTS, sub-frame offset 0 stands for the first SC-FDMA symbol in the UpPTS, and sub-frame offset 1 stands for the second SC-FDMA symbol in the UpPTS; when there is one SC-FDMA symbol in the UpPTS, sub-frame offset 0 or 1 stands for the only SC-FDMA symbol in the UpPTS.
Circumstance 2, the SRS period is great r than 2 ms, and one SRS period TSRS contains
      T    SRS    5half-frames:
(1) When sub-frame offset Noffset satisfies (Noffset mod 5)≦1,
If there are two symbols in the UpPTS, then Noffset mod 5=0, 1 stand for the first and second SC-FDMA symbol in the UpPTS within the
      (                  ⌊                              N            offset                    5                ⌋            +      1        )    thhalf-frame respectively;
If there are two symbols in the UpPTS, then Noffset mod 5=0 or 1 stands for the only SC-FDMA symbol in the UpPTS within the
      (                  ⌊                              N            offset                    5                ⌋            +      1        )    thhalf-frame;                (2) When sub-frame offset Noffset satisfies (Noffset mod 5)>1, Noffset denotes the ((Noffset mod 5)−2+1)th uplink sub-frame of the        
      (                  ⌊                              N            offset                    5                ⌋            +      1        )    thhalf-frame of SRS in a SRS period.
Currently, SRS transmission times are calculated according to Formula nSRS=└(nf×10+└ns/2┘)/TSRS┘. When the SRS period is greater than 2 ms, the SRS transmission times calculated with this formula may meet requirements, but when SRS period is 2 ms, the SRS transmission times that calculated with this formula are discontinuous. For example, for configuration 0 in Table 6, when a wireless frame has two transition points from downlink to uplink, the SRS have the same SRS transmission times on the two symbols of UpPTS
      (                  namely        ⁢                                  ⁢        sub        ⁢                  -                ⁢        frame        ⁢                                  ⁢        1            ,                        ⌊                                    n              s                        2                    ⌋                =        1              )    ,there is no continuous increment, not to meet the requirements.
Currently, when the SRS period is 2 ms, no effective solution is available to solve the problem of that the calculation result of SRS transmission times is discontinuous yet.